Processes for making contact to differently doped regions in a silicon substrate of a semiconductor device where the doped regions are disposed at different depths in the silicon substrate, and the resulting semiconductor devices are well known in practice. In such processes and devices, the silicon substrate typically includes a first region with a first dopant concentration and/or conductivity type, disposed within a second region with a second dopant concentration and/or conductivity type where the second region extends farther into the silicon substrate than the more shallow first region. In order to make contact to both the regions, a metal layer is deposited on the shallow first region. Through a heat treatment process, contact is established between the shallow first region and the metal layer. To make contact to the more deeply located second region, an additional region is formed in the shallow first region. The additional region is connected to, and is of the same conductivity type as, the deeper second region. Thus, during the heat treatment, contact can also be made to the deeper second region through the metal layer. This process is used, for example, in the fabrication of DMOS transistors. In that case, the semiconductor substrate is lightly doped n-type, the deeper second region is lightly doped p-type, and the shallow first region is heavily doped n-type. To make reliable, low-resistance contact to the lightly p-type doped, second region, the contact region formed in the first region is heavily doped p-type. The formation of this heavily p-type doped region requires an additional masking step in which exact alignment is of great importance, for the position of the additional region determines the size of the remaining portions of the first region, and thus, the properties of the diode formed by this first region and the second region. Accordingly, the deposition of the additional region for making contact to the second region is a very critical step.
It is, therefore, the object of the present invention to provided an improved and simplified process for making contact to differently doped regions in a silicon substrate of a semiconductor device and a semiconductor device which results from such a process.